Preformed sound-absorbing unit and method of making the same



Nov. 19, 1935. D, HALSTEAD 2,021,359

PREFORMED SOUND ABSORBING UNIT AND METHOD OF MAKING THE SAME Filed 0013. 19, 1952 IN V EN TOR.

Patented Nov. 19, 1935 UNITED STATES 2,021,359 PREFORMED SOUND-ABSORBING UNIT AND METHOD OF MAKING THE SAME Dorne N. Halstead, Brooklyn, N. Y. Application October 19, 1932, Serial No. 638,502

8 Claims.

This invention relates to a preformed soundabsorbing unit and to the method of making the same.

Pads of felted fibers, suitably strengthened and made semi-rigid by means of a binder, such as a small proportion of starch, are very effective in sound absorption. Because of the inherent weakness of such pads, the tendency to dusting, and undesired architectural effects, it is usual in acoustical construction to provide the pads with a facing element. A facing that is very commonly used is one of sheet metal provided with circular openings regularly spaced at close intervals, to admit incident sound.

For many purposes it is desired to provide a f acing of the type of plaster and to provide soundtransmitting openings of irregular shape and size, to resemble figurations in a natural product, such as some varieties of stone. Further, the openings for the transmission of sound through the face should have such irregular spacing as to mutilate effectively sound waves incident upon In using a facing that is somewhat fragile, as in the case of plaster, it is desirable also 25 that the plaster should be supported by integral union, over a large part of its back surface, with the sound-absorbing backing element and also that the facing should be strengthened and reenforced by screen wire or the like.

It is an object of the invention to provide an acoustical unit having the desirable properties above mentioned. Other objects and advantages will appear as the description of the invention progresses.

In the embodiment that is preferred at this time, the invention comprises a sound-absorbing pad, including rock wool or the like and a binder, and a facing element integrally united thereto. The facing comprises a hardened hydraulic cementitious composition provided with irregularly shaped and spaced holes communicating with the outer surface of the facing element and also with the pores within the sound-absorbing backing pad.

The invention is which Fig. 1 shows a perspective view of a preformed acoustical unit, with parts broken away for clearness of illustration;

Fig. 2 shows a cross sectional view on line 2--2 of Fig. 1;

Fig. 3 shows a perspective view of a modified form of acoustical unit, with parts broken away for clearness of illustration; and

illustrated by the drawing in Fig. 4 is an edge view, partly in section, of the structure illustrated in Fig. 3.

In the various figures like reference characters denote like parts.

There is illustrated a preformed sound-absorbing element l in the form of a pad that is porous, fibrous, and suitably semi-rigid. A sound-absorbing element that has been used to advantage is one containing felted rock wool fibers adhered together into a shaped, semi-rigid slab, by a small 10 proportion of starch binder. Such an element may be made by a method which includes forming a mixture of rock wool fibers with a dispersion of starch in hot water, suitably in the proportion of approximately 1 pounds of water, shaping the mixture in a mold with a screen bottom, allowing the excess of starch dispersion to drain from the shaped mixture, removing the drained unit from the mold, and drying and trimming the product to size desired.

Other felted fibrous materials may be used, as, for example, asbestos fibers. Also, other binders such as chlorinated diphenyl or bituminous material in limited quantity may be used. In any case, the felted fibrous product should be porous and be adapted to absorb sound incident upon a face thereof.

The sound-absorbing element is integrally united to a facing element 2 of generally plane surface that may comprise a binder of the type of a hydraulic, cementitious material and is provided with'irregularly shaped, sized, and spaced openings or pores 3 that communicate with the outer surface of the facing element and with 35 the pores within the sound-absorbing element. The hydraulic cementitious material may be Portland cement, plaster, or the like. Plaster has been used to advantage, as it sets quickly and is a material that is widely accepted as con- 40 stituting a desirable interior finish.

The unit may have beveled edges 4 and also side sealing and strengthening portions 5 of a composition like the face and integrally united to the edges of the sound-absorbing element. 45

In the modification illustrated in Figs. 3 and 4, the edges of the unit may comprise a non-porous, hydraulic cementitious portion 6 integrally united to the edges of the sound-absorbing pad and also a similar backing portion 1.

The method of making the improved products of the present invention consists essentially in molding a hydraulic cementitious composition, provided with density-reducing and pore-forming material, onto the face and, if desired, onto the pound of starch to 20 side edges and/or back of the sound-absorbing The pad is then placed with the treated surelement. The said composition is applied in face in contact with the freshly cast plaster castable form and is then allowed to harden. composition and pressed thereagainst. Under and trimmed or otherwise sized to the exact dilimited areas to which waterproofing has not 5 ...ensions desired. been applied and will not close the pol es at the This method of manufacture is illustrated by surface in the other, localized areas to which the following specific examples. the waterproofing has been applied. The re- There is first made a mixture of calcined mainder of the operations of making and finishgypsum (plaster) with a density-lowering, poreing the block may be performed as described 10 forming material, such as a small proportion of above. materials adapted to generate gas when wet with Units made by the latter method combine the water. Ground calcium carbide may be used. advantages of a facing portion which is keyed But I prefer a mixture consisting essentially of a or integrally united to the sound-absorbing 5 carbonate, such as carbonate of sodium or calelement, by penetration of the plastic composicium, and an acidic substance, such as an alum tion Within pores at the surface of the said eleor hydrochloric acid diluted with alarge volume ment, followed by its hardening in situ, and of water. In any case, the mixture of plaster which is adapted to admit sound readily to the with the materials adapted to generate a gas, such other said localized areas. Sound incident upon molding. Gas-entangling agents may also be throughout the element and is absorbed practipresent in the composition. Thus there may be cally as effectively as though it were admitted u d saponin. u r ther f am-stabilizing over the entire surface of the sound-absorbing agent, to decrease the tendency of the bubbles of element. 25 gas, when generated, to escape from the coin- The waterproofing treatment applied to the position. The castable hydraulic cementitious localized areas, while minimizing penetration of interior and with removable side and end walls, sion of sound into the finished unit. If the Water- 30 wool fibers made semi-rigid with starch binder. ta-in volatile materials but consists essentially, for 85 The length and breadth of the rock wool pad are example, of a non-volatile, soft grease or wax of sui a ly m wh l h n h rresp n in low melting point, this non-volatile material is inside dimensions of the mold, so that a sp ce i suitably caused to distribute itself, finally, over a left around the edges of the p Into this Sp relatively large area and thus to migrate in part there may be poured a hydraulic cementitious from the place of first application, by maintain 40 Co p s t like that fi s used, to f Sides 5 ing the finished block for some time at a moderof the b o of the yp illustrated in g 1 ately elevated temperature above the melting and O th co p Cast around e p d point of said material and below the temperaove e p the l or oil on the interior of the mold in which the In the eXample d d, the p er applied plaster is cast have the desired efiect of causing to the outer surfaces of the fibrous pad may bubbles of gas in contact with the greased surto decrease the porosity of the surface of the th urface of the finished article.

In order to minimize this tendency and To p 'gvjdg a maximum f t th in t fac to insure th the pores Will be p d and ing and/or edge elements of cementitious comadapted to receive incident sound over a satisitio sound-permeable reenforcing means factory proportion of the total surface of the may be disposed th th the following modification of the general Thus there may be used a foraminous mat ial, 60

such as a woven fabric, say, a wire gauze 8. The reenforcement should be provided with openings large enough and so closely spaced as to provide permeability to sound. In making a reenforced material. The cementitious material is allowed E the enforcing means y be placed over 23 harden, whereby the Voids Within the Said tne surfaces of the sound-absorbing element that aggregations are preserve Thus, before the are to be provided with a molded-on plaster fibrous pad is placed in position on the casting, layer and suitably spaced therefrom at a distance a portion of the surface of the pad is treated equal appmximately to one-half of the thickness 70 iyjth a grease il or a olution of aluminum Of the plaster layer to be applied. stearate, say, in kerosene or other volatile The Sound-absorbing element and Spaced solvent, to provide water-resistant patches of enforcing means are th n pres ag ins n small area each, averaging, say, a few square united to freshly cast plaster. inches, distributed over the surface of the pad. The fact that such metal reenforcing means 75 the facing, provides a source could not be used to advantage in a face that is to be perforated mechanically, subsequent to its being cast, provides an advantage of the present structure in which the openings are formed in a manner that avoids interference by the screen wire.

The product made in accordance with the present invention has features of advantage in addition to those that have been indicated previously.

The facing has areas that individually are dense and strong and plaster-like in appearance. The over-all density of the facing, on the other hand, is lighter than that of ordinary plaster. The irregularities in the spacing, size and shape of the openings provide not only a decorative and attractive appearance but also effective means of mutilating sound waves and facilitating their subsequent absorption in the sound-absorbing element, the pores of which are in communication with the openings through the said facing. The facing may be decorated, as by painting or lacquering, without closing the sound-transmitting openings therethrough. Furthermore, the sound-absorbing pad, being integrally united to of strength to the relatively fragile facing and minimizes the tendency of the face to crack. The whole is fireresistant.

The term waterproofing is used to include rendering a material water-resistant although not completely impervious to water.

The details that have been given are for the purposeof illustration and not restriction and many variations therefrom may be made without departing from the spirit and scope of the invention.

What I claim is:

1. A preformed structural unit comprising a sound-absorbing element of felted fibers, waterproofing material associated with a portion of the surface of said element, and a rigid facing of generally plane surface molded thereon and integrally united thereto and provided with irregularly spaced, irregularly shaped openings adapted to admit incident sound to the soundabsorbing element.

2. In making an article comprising aggregations of felted fibers defining voids in the said aggregations and an aqueous hydraulic cementitious composition, the method which comprises waterproofing the aggregations of felted fibers in localized areas, applying the cementitious composition to the said aggregations, and allowing the cementitious composition to harden, whereby penetration of the cementitious material within the localized areas is minimized.

3. The method of making an acoustical unit which comprises forming a sound-absorbing pad of felted fibers, applying a film of waterproofing material to a face of the sound-absorbing pad, applying to the thus treated face a castable composition including water, a hydraulic cementitious material, and density-reducing, pore-forming material, and then allowing the said composition to harden.

4. The method of making an acoustical unit which comprises forming a sound-absorbing pad of felted fibers, applying a film of waterproofing material to a face of the sound-absorbing pad,

applying to the thus treated face a castable composition including water, a hydraulic cementitious material, and bubbles of gas, and then allowing the said composition to harden.

5. The method of making an acoustical unit which comprises forming a sound-absorbing pad of felted fibers, applying a film of waterproofing material to a face of the sound-absorbing pad, applying to the thus treated face a castable composition including water, a hydraulic cementitious material, and a gas-generating material, and then allowing the said composition to harden.

6. The method of making an acoustical unit which comprises forming a sound-absorbing pad of felted fibers, forming a continuous film of water-repellent material over localized areas of the face of the pad, applying to the said face a castable composition including water, a hydraulic cementitious material, and a gas generating material, and then allowing the said composition to harden.

'7. A structural unit comprising a porous soundabsorbing element, localized areas on the surface of the said element provided with open pores, and a rigid sound-absorbing element at positions intermediate the said limited areas and provided with irregularly spaced, irregularly shaped, soundtransmitting openings extending through the facing member and communicating with the said open pores.

8. In making a porous article containing a binder and aggregations of felted fibers defining voids in the said aggregations, the method which comprises waterproofing the said aggregations, applying thereto an aqueous binder composition, and hardening the binder, whereby the said voids are preserved.

DORNE N. HALSTEAD.

facing member united\to the i 

